Search for: stress-distribution
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    Rolling Contact Fatigue under Influence of Residual Stresses

    , M.Sc. Thesis Sharif University of Technology Masoudi Nejad, Reza (Author) ; Farahi, Gholamhossin (Advisor)
    Rolling contact fatigue (RCF) phenomena is important in reducing the fatigue life and increasing the cost of maintenance. Accurate prediction of crack growth on wheels and the influence of residual stresses by FEM modeling can affect the maintenance planning. Therefore, investigation of rolling contact fatigue and its effect on rolling members life seem necessary. The first step to solve a rolling contact fatigue problem is the residual stress determination. In this research, wheel/rail contact is assumed. A bandage wheel with accurate geometry using finite element method is studied. For this purpose, a 3D elastic-plastic finite element model in ANSYS is conducted using model. The... 

    Analyzing of Ring Rolling Process

    , M.Sc. Thesis Sharif University of Technology Zamani Kohpanji, Mohammad Reza (Author) ; Asghari, Mohsen (Advisor)
    With the development of science and industry increasingly need for seamless and high-strength rings, the attention of many researchers and industrialists paid on the ring rolling process. Then, Studying details of ring rolling process is very important. The most important issues in ring rolling process which are not sufficiently considered are: stress components distribution in ring, real amounts of friction coefficient, pressure distribution over the rollers, required power, required torque and force, and finally the minimum thickness of the ring during the process, all of these parameters have developed as analytical functions. In the present study, the minimum possible thickness of the... 

    Elastic Contact Analysis of Two Symmetrical Punchs With a Half Plane in a Quasi-Static Condition Using Finite Element Method

    , M.Sc. Thesis Sharif University of Technology tarighati, Mohamad (Author) ; Adib Nazari, Saeid (Advisor)
    Nowadays, the use of finite element Software applications in enigineering departments has become Inevitable and commonplace. Acceptance of the necessity of using such software applications for reducing the cost of research and development does not require any evidences of financial instruments to be presented. Reducing design and manufacture time together with pseudo-empirical approach has cuased the finite element science to become a conventional designing tools.
    Since contact is the main method to apply a load on a ductile object,and stress concentration caused thereby is often a major cause of failure in mechanical parts, the issue of contact is a fundamental topic in mechanics of... 

    Development of a Anatomical Finite Element Model for Ankle Sprain and Rehabilitation Exercise Simulation and Numerical Analysis of Tension in Ligament

    , M.Sc. Thesis Sharif University of Technology (Author) ; Firoozbakhsh, Keikhosrow (Advisor) ; Farahmand, Farzam (Co-Advisor) ; Narimani, Roya (Co-Advisor)
    Foot related problems or diseases such as plan foot pain, diabetic foot, arthritic foot, pathological flatfoot, ankle sprain, bone fracture or other sports related injuries have been costing a significant amount of medical expenditure. Abnormal loading patterns and high pressure on the foot as well as improper or ill-fitting footwear are thought to be one major mechanical cause of foot problems. Most ankle sprains respond favorably to nonsurgical treatment, such as those offered by physical therapists, doctors of chiropractic, and rehabilitation specialists. A comprehensive history and examination aid in diagnosing the severity and type of ankle sprain. Based on the diagnosis and an... 

    The sliding frictional contact problem in two dimensional graded materials loaded by a flat stamp

    , Article Advanced Materials Research, 7 January 2012 through 8 January 2012 ; Volume 463-464 , January , 2012 , Pages 336-342 ; 10226680 (ISSN) ; 9783037853634 (ISBN) Khajehtourian, R ; Adibnazari, S ; Tashi, S ; Sharif University of Technology
    In this article, the sliding frictional contact problem for a half-plane which is graded in two dimensions is studied. The effect of medium properties gradient and coefficient of friction in contact mechanics of two dimensional (2D) graded materials which is loaded by a flat stamp have been investigated by developing two Finite Element (FE) models, in macro and micro scales. Discretizing the graded half-plane by quadrants for whose material properties are specified at the centroids by Mori-Tanaka method in both directions has been used to model the 2D FGM in macro scale. In micro scale, the ideal solid quadrant particles which are spatially distributed in a homogeneous matrix used to model... 

    Study on effect of residual stress distributions on kinetics of static strain aging after cold rolling

    , Article Materials Science and Technology ; Volume 27, Issue 11 , 2011 , Pages 1620-1626 ; 02670836 (ISSN) Koohbor, B ; Serajzadeh, S ; Sharif University of Technology
    In the present research, the effect of residual stress distribution on the static strain aging (SSA) phenomenon in cold rolled steel was investigated. A three-dimensional model was employed to evaluate the residual stress distributions within the rolled strips, and hole drilling experiments were also performed to verify the data obtained from the mathematical model. Hardness and tensile tests were then performed on the cold rolled samples at different temperatures and aging periods, and the results of these tests were utilised to assess SSA behaviour after different rolling programs. The results show that SSA occurs within the cold rolled steel in the employed aging period, and its kinetics... 

    An investigation of fracture geometry in hydraulic fracturing on a gas reservoir well production enhancement

    , Article Petroleum Science and Technology ; Vol. 32, issue. 2 , 2014 , pp. 150-157 ; ISSN: 10916466 Baghbanan, A. R ; Parvazdavani, M ; Abbasi, S ; Rahnama, A. R ; Sharif University of Technology
    Utilizing improved production methods have been always challenging in upstream industries. Nowadays, hydraulic fracturing is one of the most prestigious mechanical methods. Application of this method is in wells with low productivity index. Hydraulic fracturing efficiency depends on various factors, such as fracture geometry, fluid composition, and stress distribution. But some of them would be ignored, such as fracture geometry, which is neglected due to nongravity and lack of investigation of DFN statistical population assumption. The authors develop a more comprehensive methodology based on fracture geometry and aim to model one of the gas reservoirs in Iran that is naturally fractured by... 

    Plaque structure affects mechanical stress distribution within blood vessels

    , Article Proceedings of the IASTED International Conference on Biomedical Engineering, BioMed 2014 ; 2014 , pp. 239-243 Mohseni, M ; Mehboudi, N ; Abdollahi, M ; Shamloo, A ; Naghdabadi, R ; Sharif University of Technology
    The main goal of this study is to investigate the effects of plaque structure on its stress distribution. Rupture of plaque causes cerebrovascular diseases which lead to high mortality rates all over the world. Computers are powerful tools to understand the mechanism of plaque rupture. In this study, 3D fluid structure interaction simulation is constructed in ABAQUS 6.13 to clarify the relation between stress distribution of plaque and its structure. A model of common carotid artery with distributed stenosis was chosen for the simulation. To investigate the effects of plaque structure on stress distribution, thickness of fibrous cap and lipid core size were varied in the stenosis.... 

    Numerical Modeling of the Behavior of Base Plates with Various Degrees of Rigidity

    , M.Sc. Thesis Sharif University of Technology Shafieifar, Mohamad Reza (Author) ; Khonsari, Vahid (Advisor)
    Connections have a crucial role in the behavior of every structure. Amongst various types of connections used in steel structures are those used to connect the columns to the foundations, namely Base Plates. As other types of connections, base plates control the behavior of the structure in various respects including affecting the effective length of columns. The main task of any base plate is to distribute the forces of the column on the foundation in such a manner that the stresses in concrete are below their allowable values. Different configurations, with or without various attachments, are used for designing the base plates hence achieving various types of behavior with various levels... 

    , M.Sc. Thesis Sharif University of Technology Kashani, Massoud (Author) ; Moghaddam, Hassan (Advisor)
    The paper presents the results nonlinear analysis of steel base plates subjected to different combinations of axial and bending forces. The bending forces range from small moments representing small eccentricities to large moments from seismic actions. The results of analyses proved to be in good agreement with experiments. The parameters investigated in this study are as follows: distribution of strain and stresses in the concrete foundation and the steel plate, the strains and stresses in the tensile anchorage bolts, the location of neutral curve under the base plate, the centre of compressional reaction forces in concrete, the flextural rigidity of the base plate connection, and the axial... 

    Evaluating the Effect of Crumb Rubber on the Fracture Properties of Asphaltic Materials Using a Standardized Composite

    , M.Sc. Thesis Sharif University of Technology Ghanbari, Amir (Author) ; Motamed, Arash (Advisor)
    Fatigue cracking has a major impact on the performance of flexible pavements. Many test methods have been established to evaluate and estimate the fatigue life of asphaltic materials. Most of these test methods cannot successfully examine the fatigue properties of asphaltic materials. Recent studies demonstrate that using a standardized composite, which consists of glass beads and asphalt binder, can simulate the stress states that binder experiences in the field. This research used standardized composite to investigate the effect of crumb rubber on the fracture properties of asphaltic materials. To validate the test results, the authors conducted fracture tests on the Fine Aggregate Matrix... 

    A comprehensive experimental and numerical study on redistribution of residual stresses by shot peening

    , Article Materials and Design ; Volume 90 , 2016 , Pages 478-487 ; 02641275 (ISSN) Mahmoudi, A. H ; Ghasemi, A ; Farrahi, G. H ; Sherafatnia, K ; Sharif University of Technology
    Elsevier Ltd  2016
    Shot peening is one of the most effective surface strengthening treatment technologies in which compressive residual stresses are induced beneath the specimen surface. Effects of various factors on the distribution of residual stress profile induced by shot peening have been investigated by many researchers. However, initial residual stresses are one of the important factors which affect the shot peening residual stress.This study is aimed to present comprehensive numerical and experimental study on the effect of initial residual stresses on the shot peened specimen. Initial residual stresses were induced using a four-point bending rig and grinding. Incremental center hole drilling (ICHD)... 

    Axisymmetric circular indentation of a half-space reinforced by a buried elastic thin film

    , Article Mathematics and Mechanics of Solids ; Vol. 19, issue. 6 , 2014 , p. 703-712 Ahmadi, S. F ; Eskandari, M ; Sharif University of Technology
    The analytical treatment of an axisymmetric rigid punch indentation of an isotropic half-space reinforced by a buried extensible thin film is addressed. With the aid of appropriate displacement potential functions, Hankel transforms, and some mathematical techniques, the mixed boundary value problem under consideration is reduced to a Fredholm integral equation of the second kind. The most interesting results of the problem, including the equivalent normal stiffness of the system and the contact stress distribution beneath the rigid punch, are expressed in terms of the solution of the obtained Fredholm integral equation. Some limiting cases corresponding to inextensible and extremely... 

    Residual stress analyses of re-autofrettaged thick-walled tubes

    , Article International Journal of Pressure Vessels and Piping ; Volume 98 , 2012 , Pages 57-64 ; 03080161 (ISSN) Farrahi, G. H ; Voyiadjis, G. Z ; Hoseini, S. H ; Hosseinian, E ; Sharif University of Technology
    Elsevier  2012
    In this paper the effect of the re-autofrettage process on the residual stress distribution at the wall of a thick-walled tube is considered. For accurate material behavior modeling, it is assumed that the yield surface is a function of all the stress invariants. Also for estimating the behavior of the material under loading-unloading process, a modified Chaboche's hardening model is applied. For evaluation of this unloading behavior model a series of loading-unloading tests are conducted on specimens that are made of the high strength steel, DIN1.6959. In addition the finite element simulations are implemented to simulate the re-autofrettage process and to estimate the residual stresses.... 

    Thermo-mechanical analysis of rotating disks with non-uniform thickness and material properties

    , Article International Journal of Pressure Vessels and Piping ; Volume 98 , October , 2012 , Pages 95-101 ; 03080161 (ISSN) Hassani, A ; Hojjati, M. H ; Mahdavi, E ; Alashti, R. A ; Farrahi, G ; Sharif University of Technology
    Elsevier  2012
    Theoretical and numerical analyses of rotating disks with non-uniform thickness and material properties subjected to thermo-mechanical loadings have been carried out by variable material properties (VMP), Runge-Kutta's (RK) and finite element (FE) methods. The material is assumed to be elastic-linear hardening. A power form function is used to describe the temperature gradient with the higher temperature at outer surface. Von-Mises theory has been used as failure criterion. The effects of geometry, material and thermal loading parameters as well as boundary conditions on radial, hoop and equivalent stress distributions which have not been studied in much detail in previous works have been... 

    Numerical simulation of induction hardening of torsion bar

    , Article Proceedings of the World Congress on Engineering 2011, WCE 2011, 6 July 2011 through 8 July 2011 ; Volume 3 , July , 2011 , Pages 2080-2083 ; 9789881925152 (ISBN) Norouznejad, H ; Farrahi, G. H ; Sharif University of Technology
    In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is to compare the experimental residual stress fields measured by X-ray diffraction with those predicted from finite element modeling of the whole induction surface hardening process. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the fatigue loading, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress distribution and optimize the process,... 

    Kinetics of static strain aging after temper rolling of low carbon steel

    , Article Ironmaking and Steelmaking ; Volume 38, Issue 4 , 2011 , Pages 314-320 ; 03019233 (ISSN) Koohbor, B ; Serajzadeh, S ; Sharif University of Technology
    In this study, static strain aging behaviour of cold rolled steel strips was considered with emphasis on the distribution of residual hydrostatic stress developed during temper rolling. In order to assess residual stress distribution produced by the temper rolling, a three-dimensional model was first employed. Then, samples were rolled at a reduction of 4% under single and double pass rolling programmes and the kinetics of static strain aging phenomenon as well as the required activation energies were then evaluated using hardness and tensile tests on the deformed samples. Considering the predicted residual hydrostatic stress distribution, it was found that tensile hydrostatic stresses... 

    Numerical study of the workpiece rotation effect on the strain and residual stress distribution in the cold radial forging process

    , Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 4 , 2010 , Pages 785-792 ; 9780791849187 (ISBN) Afrasiab, H ; Movahhedy, M. R ; Sharif University of Technology
    Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. In this study, the effect of the workpiece rotation (the circumferential feed) on the strain and residual stress distribution in the inner surface of the tube in the cold radial forging process is investigated using nonlinear three dimensional finite element modeling. To verify the model, the predicted radial forging load is compared with the published experimental data which shows a good agreement. It is shown that for achieving a more favorable residual stress distribution in the workpiece inner surface, the rotation angle... 

    Investigating the effect of Casimir and van der Waals attractions on the electrostatic pull-in instability of nano-actuators

    , Article Physica Scripta ; Volume 82, Issue 4 , 2010 ; 00318949 (ISSN) Soroush, R ; Koochi, A ; Kazemi, A. S ; Noghrehabadi, A ; Haddadpour, H ; Abadyan, M ; Sharif University of Technology
    This paper investigates the effect of dispersion (van der Waals and Casimir) forces on the pull-in instability of cantilever nano-actuators by considering their range of application. Adomian decomposition is introduced to obtain an analytical solution of the distributed parameter model. Dispersion forces decrease the pull-in deflection and voltage of a nano-actuator. However, the fringing field increases the pull-in deflection while decreasing the pull-in voltage of the actuator. The minimum initial gap and the detachment length of the actuator that does not stick to the substrate due to van der Waals and Casimir attractions were determined. Furthermore, the proposed approach is capable of... 

    Buckling analysis of tapered composite beams using a higher order finite element formulation

    , Article Journal of Reinforced Plastics and Composites ; Volume 29, Issue 17 , 2010 , Pages 2663-2683 ; 07316844 (ISSN) Zabihollah, A ; Ganesan, R ; Sharif University of Technology
    Tapered composite beams are increasingly being used in various engineering applications such as helicopter yoke, robot arms, and turbine blades. In the present work, the buckling analysis of laminated tapered composite beams is conducted using a higher order finite element formulation. In tapered laminates, the material and geometric discontinuities at ply drop-off locations lead to significant discontinuities in stress distributions. Higher order formulation ensures the continuity of the stress distribution through the thickness of a laminate as well as across the element interfaces, which is very important for the analysis of tapered laminates. In addition, higher order finite element...